It is hoped that a solar cell contributes to prevention of global warming since the amount of carbon dioxide emission per power generation is small and it does not need any fuel for power generation. Currently, among solar cells in practical use, a mono-junction solar cell prepared with a single-crystal silicon or a polycrystal silicon and having a pair of p-n junction has become mainstream, and researches and developments regarding solar cells having various kinds of configurations have been proceeded in order to achieve a high performance of the solar cells.
As a material of a solar cell, a semiconductor including a localized level or an intermediate band in a forbidden band has been proposed until now. By employing such a semiconductor, in addition to making a configuration in which electrons are excited from a valence band to a conduction band, it is possible to excite electrons from the valence band to the localized level or the intermediate band, and from the localized level or the intermediate band to the conduction band. That is, since it becomes possible to absorb light having a lower energy than an energy corresponding to the width of the forbidden band, it is considered that it is possible to achieve a high performance of a solar cell by using a semiconductor including a localized level or an intermediate band in the forbidden band.
As a related art of the solar cell described above, Patent Document 1 for example discloses a p-n junction solar cell including an n-type semiconductor laminated to a light-entering side of a p-type light absorbing layer, the n-type semiconductor having a wider forbidden band than that of the p-type light absorbing layer, wherein the p-type light absorbing layer has a localized level or an intermediate band in its forbidden band. Patent Document 1 discloses an example in which the p-type light absorbing layer is defined as ZnTe1-xOx, and the thickness of the ZnTe1-xOx is determined as 1000 nm. Also, Non-Patent Document discloses a technique for producing GaNAs by means of continuously supplying nitrogen, the GaNAs being a semiconductor including a localized level or an intermediate band in a forbidden band in the same way as in ZnTe1-xOx.